NFC: st21nfca: Fix st21nfca_gates offset

It is useless to start from index 0 when looking for a gate
because only dynamic pipes are retrieved with
ST21NFCA_DM_GETINFO(ST21NFCA_DM_GETINFO_PIPE_LIST).

The first dynamic pipe is present at index 3.

Signed-off-by: Christophe Ricard <christophe-h.ricard@st.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>